Elastomeric silicone foams are well known and have a variety of uses, including thermal insulation, electrical insulation, flame barrier, cushioning applications, etc. Elastomeric silicone foams have excellent physical properties and in addition to the above uses are suitable and desirable for use in many additional applications. However, there is a problem with addition cured elastomeric silicone foam that the viscosity of the composition prior to blowing and cure cannot be reduced simply by reducing the viscosity of the inputs. Particularly, such foam cured from vinyl end-stopped polydiorganosiloxane will split and tear during the foaming process where the viscosity of the polydiorganosiloxane is too low.
In the past the inventors herein have relied on solvents or diluents to reduce viscosity. However, this method of viscosity reduction leads to solvent emission problems as well as bleed.
The instant invention is best understood with knowledge of prior art foam references. U.S. Pat. No. 3,923,705, Smith, discloses that elastomeric silicone foams may be produced with a single reaction that both cross-links to cure the composition as well as produces hydrogen gas to blow the foam. This reaction takes place between a silanol and silicon hydride. Optionally, there can be added a vinyl containing silicone that will simultaneously cross-link through addition with a silicon hydride without gas generation. Obviously, this is a convenient method to produce silicone foam.
U.S. Pat. No. 4,189,545, Modic, produces silicone foam compositions by adding water. For example, water could be added to a composition of a vinyl containing siloxane, a hydride containing siloxane and platinum to generate gas at a rate only indirectly related to cross-linking rate. The water reacts with hydride containing siloxane to produce hydrogen gas and silanol. Silanol reacts with hydride containing siloxane to cross-link and produce a second molecule of hydrogen gas. A vinyl addition reaction with silicone hydride will cross-link the composition simultaneously.
U.S. Pat. No. 4,418,157, Modic, reduces density and strengthens silicone foam by adding a resinous copolymer. U.S. Pat. No. 4,599,367, Baumann, et al., reduces density by using a combination of silanol and water. U.S. Pat. No. 4,762,859 reduces foam density by the addition of nitrogen containing compounds.
It is an object of the present invention to produce low viscosity, foamable silicone compositions which do not bleed and which do not split and tear with foaming.
It is a further object of the present invention to produce a foamable silicone composition which will flow easily into crevices and will easily conform to the shape of a mold.
These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.